As a result of the rapidly growing energy needs of modern life, the development of high performance energy storage devices has gained significant attention. Supercapacitors are promising energy storage devices with properties intermediate between those of batteries and traditional capacitors, but they are being improved more rapidly than either. Over the past couple of decades, supercapacitors have become key components of everyday products by replacing batteries and capacitors in an increasing number of applications. Their high power density and excellent low temperature performance have made them the technology of choice for back-up power, cold starting, flash cameras, regenerative braking and hybrid electric vehicles. The future growth of this technology depends on further improvements in energy density, power density, calendar and cycle life and production cost.